Microkinetics modeling of the hydro-isomerization of n-hexane

The hydroisomerization of n-hexane over platinum-loaded mordenite and ZSM-5 was simulated using a microkinetics approach. Alkoxy species were assumed to be the reactive intermediates. Carbenium ions were considered to be part of the transition state. This leads to true activation energies of isomerization of approx. 130 kJ/mol for both zeolites. The model explicitly takes into account the variation in micropore filling. This enables modeling of the orders of the reaction over a wide pressure and adsorption enthalpy regime. The resulting model describes exptl. measurements very well. It is shown by both methods that ZSM-5 is more active per acid site than Mordenite due to its higher adsorption enthalpy for n-hexane. The effect is small because of the low hexane order. The adsorption entropy plays a decisive role in detg. the overall activity